Slow POP3 with Dovecot and/or Courier

I've got a problem with POP3 access on my server. The access to the mails is rather slow. I am using Outlook XP on Windows for retrieving the mails, and it seems to "pause" slightly after each email. All emails are downloaded fine, and there are no timeouts, however it takes up a lot of time.

I have tried both Dovecot and Courier on the server. This is an issue with TLS or without TLS. I am authenticating against plain UNIX users (basically changed nothing in the configuration scripts, except the TLS cert). This is on a relatively unchanged Suse 9.3 system.

No error or warning messages in the log.

I am really at a loss here - what could possibly cause this problem? The server should be a lot faster than this (3 GHz, plenty of RAM, fast Internet connection).

My previous server was less capable and worked fine, also with Outlook, same setup (also with courier, but on Debian). I just can't seem to find the relevant difference...

I tried using Thunderbird for a change, with the same result. I have also verified that the CLIENT seems to pause after each email, i.e. before sending the next "RCPT x" command to the POP server. (some 0.3 seconds to 1 second delay).